vlaiv

As far as I understood Olly - he claims that star size don't correlate with background detail in RASA data - that somehow stars are being large / soft (sign of high level of blur - high FWHM) - but that detail is still there in the background.

I'm not sure diffraction spikes are good comparison point. Their intensity is always percentage of brightness of the source that is creating them. They are equally present on stars as they are on extended objects like planets. Take image of Jupiter taken with reflector with spider, and stretch it very hard - you will get diffraction spikes from planet as well. We just don't see them because intensity needed to notice them is very very large and comes from brightest stars only in normal stretch levels. Here is old planetary capture of mine extremely stretched: Besides that strange circular feature that I think is refection of a barlow lens used and shows aperture of the telescope (some unfocused light) in top corner - spikes are starting to show But back on issue of blur - FWHM is the same for star and for nebulosity and nebulosity simply won't show features that are that order of size or smaller - due to blur. FWHM is important bit. That and how much high frequency components there are (or are expected) in signal itself. Take uniform light without variation - no matter how much you blur it - it will look the same. Sky in daytime photo for example - if it's clear and there are no clouds - it will look the same in sharp and in blurred image. If you expect smooth varying nebulosity and that is what you get - you might think it was not affected by blur in the same way stars were - but you'd better check other sources to verify if nebulosity is indeed smooth or not.

I can't really convince you that this is indeed so if I don't start with highly technical stuff and math. Best I can do to show you that this is in fact true (without going into technical stuff) is to do the following: I do hope we are in agreement that for all intents and purposes stars in astronomical image are in fact point sources (before the light reaches earth's atmosphere and aperture of telescope). Imagine following scenario to understand what a blur is - there is only one star in the sky and nothing else - no light pollution, no nebulosity, nothing. Photons from this star always arrive from same angle in the sky - from same point, and in perfect world - they would all be focused into same spot, right? However, we have atmosphere, we have aperture of telescope and we have aberrations. All of these conspire together against our poor photon so it does not land on a single point but gets thrown randomly around this point. Every photon that comes from this star gets the same treatment - majority of them are thrown off course just a bit, some are thrown off course a bit more. When they all accumulate - we get nice bell shaped distribution of photons with certain FWHM. In some scopes it will be nice gaussian like shape - where seeing dominates over diffraction effects, while in other scopes we won't get nice gaussian type shape but it will still be sort of bell shape but little distorted - this is where aberrations dominate seeing (seeing should be fully random and produce true gaussian shape - others are predictable and produce different shapes and result is combination). Ok, now that we know how star light behaves - it gets scattered in particular way around that single point - we will call this "blur" as it blurs star into some non point like shape. Punchline - atmosphere, telescope, sensor - all of them have no idea if that photon came from a star or from nebulosity or from some galaxy. All photons will receive the same treatment. Every point in the image will be blurred regardless of the source of photon - it is just important that photon arrives from same spot in the sky and it will get scattered around in that bell shape. Do this with every point of the image and you have blurred image - that is how blur works - it performs above operation on every single point of the image. Again - all the participants that scatter photons around from its true position have no clue if photon is coming from a star or from somewhere else - they will treat it the same.

What affects the stars equally affects the nebulosity. Star is just "shape of the blur" affecting the whole image. If there were no blur affecting the image - every star in the image would be single point of light (as they are from this distance. While you can "fix" the stars - using some of the morphological tools - you can't fix the nebulosity that way. Closes thing to fixing the image is sharpening that is performed on the whole image and not stars alone. How much it fixes the image can be seen in stars - if stars look better - then whole image will look better after sharpening. Morphological tools "reorganize" bright pixels - and do so only with and around stars (like "make stars round" action and alike). They are not sharpening tools.

I think that RASA is very good / excellent in what it does - don't get me wrong. It is just that I'm not so sure about One imaging scope to rule them all part - for my style, I would not choose RASA - even for imaging alone, and we haven't touched other "disciplines" related to data capture - like solar / lunar / planetary imaging, spectroscopy .... For me - there is too much lack of sharpness in RASA, and that's coming from RC owner - those scopes have massive secondary obstruction.

Up to a point - it really fast gets into territory of diminishing returns.

Yes it is. It did not used to be, but with recent price rise it is now quite expensive. When I purchased it, it was about £150 or so.

Ok, let's do a comparison of say RASA 8" and EdgeHD8" or RC8" scopes. In either case you sacrifice something, question is - what you want to sacrifice. RASA8" simply can't do high resolution work properly. Other two options can. RASA8" is fast, but other two scopes are equally fast - so this is a tie (speed is not F/ratio - speed is aperture at resolution and all scopes are 8" so it is only the question of matching resolution between them - RASA is 400mm and other scopes are 2000 and 1600mm respectively so matching resolution is really a piece of cake - one just needs to use correct bin factor). RASA8" can do wide field - while other two can't. While this is technically true - one can go around it. If you want to make wide field image with EdgeHD 8" or RC8" you can and it won't be lower quality than one produced with RASA8". So what is the score: Tied on one point, RASA leads on one point - but other two scopes can match it if used in certain way with only time as being cost to do so, and RASA looses on one point - but this time without possibility to match other two scopes - no matter how much you try - you simply need to accept lower resolution of that optics. Given what I've said above - how is RASA possibly the best choice?

I think that simplest way to get max field on that scope (even if it means straight thru viewing) is to get 56mm plossl EP. Exit pupil won't be much bigger than using 32mm plossl on F/6 scope - and that, depending on how dark are your skies, is quite acceptable (to me at least). FLO has that EP in Astro Essential variant. I just used what I had on hand, but it looks like that reducer is no longer affordable - it costs about x3 as much as mentioned EP. https://www.firstlightoptics.com/reducersflatteners/ts-optics-ccd-telecompressor-for-ritchey-chrtien.html and you still need to pair it with suitable eyepiece - one with ~30mm of field stop (mine has 30.8mm and this reducer fully illuminates ~29mm).

Well, if you can't use 2" diagonal - that is going to be a problem. This solution depends on that and I think that reducer would be vignetted on 1.25" connection. My scope is SkyWatcher Evostar 102 achromat. I did upgrade focuser on it - I replaced the stock one with M90 TS monorail that I had left over from my RC8 focuser upgrade. This focuser is a bit shorter than stock focuser so I use 35mm 2" extension before diagonal because focuser has only 50mm of travel (stock one has at least double that). This is for 2" diagonal of course. For 1.25" I would surely need longer extension to be able to focus. Good thing about this adaptation of reducer is that it virtually does not need focus position change on my setup. Reducer requires about 50mm of inward travel when working on prescribed reduction (x0.67) and removal of eyepiece barrel and direct connection to diagonal recovers those ~50mm - so focus pretty much remains in same place (only minor tweak needed). With Tal - you'll probably need to shorten the tube and I guess you'll be reluctant to do that (I know I was on my scope - it was an option, but I decided against it).

Olly, if you really want to see if RASA can be compared to even 80mm scope - point it to the moon and try to match 80mm in resolution of the image on the moon.

left is 6" + 4" data - which should be less "resolving" than 8" data.

But is it as sharp as can be produced by 8" optics at "400mm" of focal length (or rather at that resolution)

I did a little experiment and it seems to have worked, so if anyone wants to do similar, here are details. I adopted CCD47 which is CCDT67 copy - a telecompressor / reducer originally intended for imaging - but works with F/9 and slower scopes with relatively flat field, to my achromat refractor. Issue with this and any other reducer is that it requires certain distance from eyepiece to be of prescribed reduction factor. It also moves focus inward - which makes them hard to use for visual. I decided to try to adopt it to 2" diagonal that I have together with my go to low power eyepiece - ES68 28mm. Adaptation required removing both nose pieces - that of diagonal and that of Eyepiece and also removing 2" receptacle of diagonal. Diagonal has 2" SCT female thread, while both eyepiece and reducer have male M48 on their side. Since there are no readily available adapters for this combination - I resorted to 3d printing (and yes, even if there were adapters to be purchased - I just love 3d printing ). Here is the result: It did not come without some issues - I over tightened one of the adapters and besides some minor tool marks on equipment - there might be issue with diagonal now (It was heated up to certain temperature to soften the plastic to be able to unscrew it - not sure if this messed up with the mirror due to thermal expansion) and also - let's say that Argon purged title on the eyepiece is no longer telling the truth Trying to unscrew adapter lead to actually unscrewing internals of the eyepiece. I'm sure it's still fine - but I'm also sure that its no longer argon filled (if it was before). Overall - reduction works. I only managed daytime tests and some lunar testing. Center of the field is sharp and there is minor sharpness fall off towards the edge - maybe outer 15% or so is not as sharp. Craters on the moon are still there and all - it is just that image is a bit softer in that region. Not sure what the stars will be like - hope to test it soon. In this configuration there is no significant change in focus position as eyepiece is moved forward by about 50 mm - length of 2" receptacle that was removed. Nice way to get wide(r) field scope from 100/1000 achromat - here is FOV diagram: Red is ES68 28mm without reducer, yellow is with reducer and green is max FOV for 2" eyepiece in this scope (56mm 52 degree plossl - with assumed 47mm field stop).

I downloaded it and opened it in LibreOffice and it looks legit (I did not notice anything suspicious). It is however far removed from user friendly. Did not even want to start to do any sort of calculation with it Btw, @laurent-rattini Hi and welcome to SGL. Maybe if you simplify things a bit? Maybe some sort of custom software or at least video on how to use spreadsheet?

From a brief look, it seems that this interpretation deals nicely with one thought experiment about causality and non locality. Imagine Alice and Bob having a pair of entangled particles. Alice and Bob are separated in space and they both measure their respective particle at some point. Stationary observer with respect to A and B would say that it happened in quick succession. Special relativity tells us that order of events is observer dependent. So there is observer which "sees" Alice take the first measurement and Bob has his particle "already collapsed" into some state by measurement done by Alice. Vice verse - there is observer that concludes the opposite. So who performed "the collapse"? As far as I can tell, transactional interpretation has both forward and backward propagating wave - so it is compatible with above. In such scenario - it does not matter who did it first as both "waves" were sent and their exchange is actual transaction that caused "wave function collapse". It also is compatible with quantum field theory where things are disturbances in quantum fields - so fields must be element of reality and thus waves in those fields are elements of reality (which transactional interpretation implies). Only thing that I'm sort of baffled with is that this interpretation does not address where probabilities arise from. I guess it treats them with propensity approach (again, I'm slightly troubled with this - but if that is the way world works, hey, it's the way world works ... ).

In case anyone cares, I have a new favorite interpretation of QM (and I wonder how I did not come across that earlier): https://en.wikipedia.org/wiki/Transactional_interpretation

I just think that many worlds is interesting because: a) I really like it, it is elegant b) it fails to explain frequency of outcomes We can learn something from all of this, I believe. One obvious thing would be to assert that one of axioms of this interpretation is simply wrong. Other would be to reconsider our understanding of probability and what it means.

Ok, now that is an "explanation" Now we have a measure of existence of a world Ok, let me put it this way. I'm going to exaggerate a lot here - but just to get my idea across. We prepare electron with a spin in a such way that probability of it being a spin up 0.999999999999... (and now imagine one hundred nines behind the first zero - or in another words - "ridiculously" high probability). Now we perform an experiment with such electron and we get world wave function to be in superposition of <electron up and we measured it up> and <electron down and we measured it down> Now one copy of us is already raising their brow - now what a coincidence - we just achieved experiment result with spectacularly small probability - but that is ok because we "don't exist" that much Now we repeat the experiment - both copies. We now have 4 copies in superposition. One copy is on the floor laughing since they measured such an unbelievable odds twice in row - and they just feel fading out of existence 2 of remaining 4 copies - have now their eyebrow raised, again not believing their luck and feeling like they are starting to "vanish out of existence" or something Only remaining copy is happy as they are - having strong measure of existence. See where I'm going with this - and how ridiculous that explanation is - measure of existence of a world. It is component of super position of wave function and as such, if we accept global wave function to be item of reality (and many worlds strongly does so) - one part of it can't be more existing than others - they all exist.

Well, that is common wisdom, and according to that - they do make same predictions, but for example - I've outlined where many worlds fails to reproduce experimental results. I must admit that I haven't read the original paper, so I might be assuming something wrong in the case I outlined - but I'm not the only one to spot the said problem at least according to this:

Is there any particular interpretation with least or perhaps none objections? No matter how "crazy" or "not elegant" it may be?

I just love many world interpretation and I think that most people don't understand the gist of it, but it simply has a problem that I can't find a way around that tells me it's not (in part or entirely) the explanation. Here is condensed / simple version of the problem: Take any event that has two outcomes (polarization of photon or spin of electron) and create setup with different probabilities than 50:50. That is very easy to do - just take electrons with spin that is at certain angle to electric field (not 90 degrees). Each time we perform one experiment world "splits" or shall we say global wavefunction turns into superposition of two new sets of states (history + new measurement up and history + new measurement down) - if you do enough of these - being in one "history chain" will determine probability - but that probability always splits as 50:50 and not by angle - so we can't justify experiment results by being on random branch as any random branch will have history consistent with 50%:50% split and not say 90%:10% If many worlds interpretation is correct - we would always 50%:50% probability of spin up vs spin down - no matter the angle as there is no "assigned weight" of being one versus the other "copy". Two outcomes create two copies and being either of them is equally likely.

Oh, it is very simple It can be phrased like this: Why, oh why did I measure only one value when QM tells me that system is in superposition of countless possible values - but I never seem to measure that. Why do my measurements relate to square of amplitude of QM wavefunction (probability of outcome is square of amplitude)? But most importantly - why do we never see super position, is it a real thing or just calculation aid?

Last that I've head about in that field is using electron spin to record the data. It was hot research area some time ago, it has a catchy name as well - let me see if I can find it. https://en.wikipedia.org/wiki/Spintronics yep, spintronics it is

It is really mind boggling that we still don't have any conclusion regarding that or accepted interpretation of QM